The invention relates generally to winding equipment and more specifically to a method and apparatus for uniformly winding elongate sheets of material onto hubs or reels.
The diversity and specialization of packaging materials generally necessitates that they be manufactured at a site distinct from their site of utilization. For example, the mills which produce cardboard boxes and plants which produce molded containers, almost without exception, are distinct and distant from the sites at which products are placed in such containers. This rather obvious business reality encourages manufacturers of containers or packaging material to routinely examine how a given material may be compacted, collapsed or in some other fashion rendered more dense in order to improve the economics of transporting same from the manufacturing site to the utilization site. Due to this and other considerations, the design phase of preparing such material for shipment and the equipment related thereto has become a technology in itself.
A typical example of a package or packaging material which is fabricated at one location and shipped to another for application is the plastic carrier utilized for grouping six or eight beverage containers such as metal cans or glass bottles into a readily grippable and transportable package. The plastic carrier is manufactured in a continuous elongate sheet having spaced-apart apertures punched therein which both receive the beverage containers and define straps or webs which are readily engaged by the fingers of a hand. The plastic sheet is punched and prepared in a continuous length and then cut and reeled onto hubs or reels for shipment to a beverage bottler or similar facility where the sheet is cut into short lengths and installed upon groupings of bottles or containers.
Upon cursory examination, the operation of coiling the lengthy sheets or strips of the plastic material onto reels or hubs would appear to be simple and without difficulty. Upon closer examination, however, it will be appreciated that the material subsequent to punching more resembles lattice-work than a sheet, i.e., more of the material has been removed by the punching operation than remains. The material therefore lacks lateral and diagonal stability and exhibits uneven and unpredictable winding characteristics. Depending upon the amount of material remaining and thus the structural integrity of the sheet, an acceptable wind can sometimes be achieved by careful and accurate sizing of the internal width of the hub to the width of the elongate carrier sheet. Such a step is an obvious and relatively simple expedient to ensure that the strip does not skew, fold or slip inwardly along one edge toward the core of the hub or reel.
This approach, however, may not be successful if the ratio of the amount of removed material to that remaining is high. In this case, random stacking of punched area upon punched area, punched area upon web and web upon web results and causes highly irregular diametral variation as the material winds onto a reel. Aside from the obvious unattractiveness of such a wind, the diametral variation can create difficulties during the packaging process when the material is unreeled, can result in a reduction in the total length of material disposed upon a reel and, finally, can render the material difficult to use since it may eventually warp or deform from the desired planar configuration if stored in this condition. While it is true that as the material winds onto the reel, the length of a single wind, i.e., the circumference, slowly increases as the radius from the center of the reel or hub increases, this slowly changing parameter has generally been found to exacerbate the problem of radially uneven winding rather than reduce it.